The invention relates to photovoltaic cells, and more particularly, to methods for manufacturing a contact grid including bus bars on a photovoltaic cell.
Current photovoltaic cells such as solar cells are covered with a metallic contact grid for transporting current and minimizing current loses due to resistance through underlying silicon-containing layers. The patterns of conductive metal lines that define the metallic contact grid and/or bus bars are generally screen printed using thick film technology to layer a conductive paste of metal materials into a desired pattern. The metal paste, typically silver, is dried and then fired, i.e., sintered, at relatively high temperatures. Problems related to current processes include the costs associated with the use of silver, which is relatively high and that the solar efficiency of the photovoltaic cell can be degraded during the annealing process because of the high temperatures currently used to effect sintering of the silver paste. For example, once the silver paste is screen printed, the annealing step typically occurs at temperatures of about 900° C. for an extended period of time, typically about an hour or more, which can cause the degradation.
Accordingly, there is a need for improved manufacturing processes that are less expensive and less prone to degradation.